Is there something I can do re revitalize long term shelving of prepared fixer?
When you approach the end of shelf life for your fixer, you can extend it by adding some sodium sulfite. How much? It's probably safe to add, say, half of what the original formulation calls for. Or if you have the ability to do a chemical analysis you could add enough to restore the original chemical concentration.
This is assuming a fixer based on thiosulfate. I don't know if there is any bad effect from adding too much, which is why I suggest adding only a conservative amount of sulfite. Now, you cannot keep adding sulfite forever; eventually the breakdown product, sulfate (SO4), will begin to hinder the speed of fixing. You can probably test for this with a "film clearing test."
...mix 60 g of crystals per liter of water, then discard after one session...
Donald, you would probably also be well-served to throw in at least a pinch of sulfite. As the thiosulfate begins to sulfurize the sulfite will restore it to thiosulfate. Without such a preservative it is possible (I don't know if it's an actual problem for immediate use) that you might end up with small amounts of sulfur trapped in the emulsion. Fwiw I used to read about Ansel Adams using a so-called plain fixer, which I presumed was like yours. I thought, of gosh, even Ansel Adams doesn't know to add some sulfite. But then... I saw, in one of his books, his formula for "plain fixer." It turns out that his "plain fixer" did indeed include sulfite. Anyway, I would say it's always a good thing to have at least a little.